1. Field of the Invention
The invention relates to polymers containing acidic groups and based on polyalkyl(meth)acrylates as a bitumen improver and to bitumens that are improved with such polymers which exhibit improved technical properties.
2. Discussion of the Background
Bitumen, which is a mixture of substantially different hydrocarbons with variable portions of paraffinic, naphthenic and aromatic hydrocarbons, has diverse applications owing to its properties. Examples include the manufacture of street surfaces, as grouting compounds, as coatings, in building protection, in the form of tarpaper and as sealing compounds against ground water.
Bitumens exhibit specific properties which are a function of the origin of the crude oil source of the bitumen. Such properties include negligible or no elasticity and coatings manufactured with them embrittle at low temperatures and soften at higher temperatures.
By adding various additives, in particular polymers, attempts have been made to achieve a hardening of the bitumen, in particular, an improvement of the rheological properties. Bitumen containing additives imparts to asphalt (a mixture of bitumen and mineral matter which is used especially for street construction) adequate stability and low temperature flexibility and a high endurance limit with continuously increasing traffic loads. Thus, the addition of polymers can enlarge the so-called plasticity gap, i.e., the difference between the softening point and the breaking point. A reduction in the breaking point (DIN 52 012) and a increase in the ductility (DIN 52 013) through the addition of polymers indicates better low temperature flexibility. The purpose of the polymers as bitumen additives is to modify the elastic viscous properties of the bitumen. This means the expansion of the plasticity gap and the improvement of elastic recovery.
In addition to natural and synthetic rubbers as polymers, thermosetting resins and thermoplastics have been tested as bitumen improvers (Korner et at., Plastics and Rubber, Vol. 24 (1977), pages 475 to 478). Styrene/budadiene (SB), EPDM and ethylene/vinyl acetate (EVA) copolymers have also been used as polymer-bitumen additives, and especially for industrial bitumen, atactic polypropylene has also been used commercially. Commercially available polymer-modified bitumens are .RTM.CARIBIT (SB, Shell), .RTM.OLEXOBIT (EPDM, BP), and .RTM.STYRELF (SB, Elf).
Polymers based on acrylates and methacrylates, in particular polymers of alkyl methacrylates (PAMA) are described as bitumen improvers. Despite good fulfillment of a number of demands imposed on them as additives, these polymers have not found wide commercial use, primarily due to inadequate improvement of the elastic recovery of ready-to-use, elastomer-modified bitumens
U.S. Pat. No. 2,420,082 describes bituminous mixtures comprising bitumen and 2 to 5% poly-C2-C.sub.10 -alkyl methacrylates, without specific data about their molecular weights, which improve the ductility of the bitumen.
U.S. Pat. No. 2,848,429 discloses bitumen mixtures that exhibit improved ductility and each of which were obtained by adding 0.01 to 0.5% rubber and poly-C.sub.8 -C.sub.24 -alkyl(meth)acrylates. The PAMA's have molecular weights ranging from 5,000 to 500,000.
The German DE-AS 12 40 773 and DE-OS 23 31 727 describe bituminous binders for street surfaces, the binders being also improved with polymers of alkyl methacrylates without any detailed and specific information about these polymers.
Furthermore, polyalkyl(meth)acrylates or copolymers of alkyl(meth)acrylates are proposed as bitumen improvers in DEOS 25 09 473. A non-sticky copolymer is described which is a solid at ambient temperature, has molecular weights ranging from 50,000 to 500,000, and is synthesized substantially from alkyl(meth)acrylates with alkyl groups which contain more than 6 carbon atoms, and from 3 to 20 % by weight of basic, nitrogen-containing monomers. Also, in German patent applications P 39 17 816.1 and P 39 25 827.0 polymers are described which contain under 2.8% by weight carboxylic acids incorporated by polymerization and under 2.8% by weight basic nitrogen compounds incorporated by polymerization. Additives polymerized stepwise by emulsion polymerization are known from the Japanese Kokai 52-141,829, and poly-C.sub.4 -C.sub.20 alkyl methacrylates having molecular weights ranging from about 5,000 to about 1,000,000 are known from WO 88/07067, and which are contained in quantities ranging from 0.01 to about 10% by weight in the modified bitumen.
Olefinic copolymers, synthesized primarily with acrylic acid or methacrylic acid as reactive comonomers, are described as additives to bituminous materials in the German published patent application 11 88 807 and in WO 87/04 174. According to German 11 88 807, when mixed with the bituminous material, a carboxyl group-containing, rubbery butadiene-acrylonitrile copolymer is cross-linked through the addition of an oxide of a divalent metal, preferably zinc oxide. According to WO 87/04 174, in addition to .alpha.-olefin homopolymers and .alpha.-olefin-.alpha.,.beta.-unsaturated carboxylic acid copolymers, ionomers of the latter copolymer type can also be used as bitumen additives. However, these ionomers have low melt flow indices and cannot be homogeneously incorporated into the bituminous material owing to their cross-linked state.
Prerequisites for polymeric additives, in order to impart improved properties to bituminous mixtures, are oxidation and thermal stability of the polymers, their easy incorporation into bitumens, compatibility with various kinds of bitumen and stability of the bitumen/polymer mixture.
The known polymeric bitumen additives adequately expand the plasticity gap in bituminous mixtures and in mineral blends manufactured with them, i.e., the softening point and breaking point of such materials are often advantageously affected by known polymer additives
The high endurance limit and elasticity of the asphalts which are manufactured with bituminous binders and which are defined by the elastic properties of the bitumens, do not yet exist to an adequate or good degree, as shown, for example, in practice by asphalt street surfaces which are severely deformed.